ASoC: dt-bindings: renesas,rz-ssi: Document RZ/V2L SoC

Document RZ/V2L SSI bindings. RZ/V2L SSI is identical to one found
on the RZ/G2L SoC. No driver changes are required as generic compatible
string "renesas,rz-ssi" will be used as a fallback.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20220227225633.28829-1-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>